IR Communication

1
IR Communication

• October 27, 2004

2
Sources

• Lindsay, Andy. IR Remote for the Boe-Bot. v 1.0
  2004.

3
How Does a TV Remote Work?

• On a button press, the remote flashes its IR LED
  on/off at 38.5 kHz to broadcast a code for that
  button.
• The code is produced by controlling the brief
  amounts of time the IR LED flashes on and off.
• It flashes a signal to indicate the start of
  transmission.
• For a SONY TV, the remote has to broadcast IR for
  2.4 ms o indicate start.
• The message that follows consists of a
  combination of 1.2 ms (binary-1) and 0.6 ms
  (binary-0) broadcasts.
• The IR detector on the Boe-Bot sends low signals
  that match the time pattern broadcast by the
  remote.

4
How Does the TV Dectector Work?

• In many cases IR detector/receiver on your
  Boe-Bot is the same detector found in many TVs
  and VCRs.
• This detector sends a low signal whenever it
  detects IR flashing on/off at 38.5 kHz and a high
  signal the rest of the time.
• When the IR detector sends low signals, the
  processor inside a TV or VCR measures how long
  each of the low signals lasts.
• These are used to figure out which key was
  pressed on the remote.
• BASIC Stamp 2 can be programmed to detect,
  measure, store, and interpret the sequence of low
  pulses it receives from the same IR detector.

5
Timing Diagram

• This message consists of thirteen negative pulses
  that the BASIC Stamp can easily measure.
• 1 the start pulse, which lasts for 2.4 ms.
• 2-13 will either last for 1.2 ms (binary-1) or
  0.6 ms (binary-0).
• 2-8 indicates which key is pressed.
• 9-13 indicate if the message is being sent to a
  TV, VCR, CD, DVD player, etc.
• Pulses are transmitted in least significant bit
  first fashion.
• the first data pulse is bit-0.
• the next data pulse is bit-1
• Etc.
• If you press and hold a key on the remote, the
  same message will be sent over and over again
  with a 20 to 30 ms rest between messages.

6
Timing Diagram
7
PULSIN Command

• Complementary command to PULSOUT
• The syntax for the PULSIN command is
• PULSIN Pin, State, Variable
• Pin the I/O pin for measuring the pulse.
• State is used to determine whether the pulse is a
  high pulse (1) or a low pulse (0).
• Variable stores the pulse duration measured by
  the BASIC Stamp.

8

• ' IR Remote for the Boe-Bot - RecordAndDisplayPwm.
  bs2
• ' Measure all data pulses from SONY IR remote set
  to control a TV.
• ' STAMP BS2
• ' PBASIC 2.5
• time VAR Word(12) ' SONY TV remote variables.
• index VAR Nib
• ' Display heading.
• DEBUG "time ARRAY", CR,
• "PWM MEASUREMENTS", CR,
• "Element Duration, 2-us", CR,
• "------- --------------"
• DO ' Beginning of main loop.
• DO ' Wait for rest between messages.
• PULSIN 9, 0, time(0)
• LOOP UNTIL time(0) gt 1000

9

• PULSIN 9, 0, time(0) ' Measure/store data
  pulses.
• PULSIN 9, 0, time(1)
• PULSIN 9, 0, time(2)
• PULSIN 9, 0, time(3)
• PULSIN 9, 0, time(4)
• PULSIN 9, 0, time(5)
• PULSIN 9, 0, time(6)
• PULSIN 9, 0, time(7)
• PULSIN 9, 0, time(8)
• PULSIN 9, 0, time(9)
• PULSIN 9, 0, time(10)
• PULSIN 9, 0, time(11)
• FOR index 0 TO 11
• ' Display 12 pulse measurements.
• DEBUG CRSRXY, 0, 4 index, "time(", DEC
  index,
• ")",
• CRSRXY, 9, 4 index, DEC time(index)
• NEXT
• LOOP ' Repeat main loop.

10
A Sample Dataset

• Test data for 5 second press of each key 0-9,
  vol, vol-, ch, ch-, power and enter.
• Dataset

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13
' IR Remote for the Boe-Bot - 2BitRemoteBoeBot.bs2
' Control your Boe-Bot with an IR remote set to
control a ' SONY TV with the 1-4 or CH/- and
VOL/- keys. 'STAMP BS2 'PBASIC 2.5 time
VAR Word(2) ' SONY TV remote
variables. DEBUG "Press hold a digit key (1-4)
or CH/- and VOL/-" FREQOUT 4, 2000, 3000
' Start/reset indicator. DO
' Beginning of main loop. DO
' Wait for rest between messages.
PULSIN 9, 0, time(0) LOOP UNTIL time(0) gt 1000
PULSIN 9, 0, time(0) ' Measure/store data
pulses. PULSIN 9, 0, time(1) ' Decide which
maneuver to execute depending on the '
combination of pulse durations stored in the
first ' two pulse measurements. IF (time(1)
lt 500) AND (time(0) lt 500) THEN PULSOUT 13,
850 ' Forward
PULSOUT 12, 650
14
ELSEIF (time(1) lt 500) AND (time(0) gt 500)
THEN PULSOUT 13, 650
' Backward PULSOUT 12, 850 ELSEIF (time(1)
gt 500) AND (time(0) lt 500) THEN PULSOUT 13,
850 ' Right rotate
PULSOUT 12, 850 ELSEIF (time(1) gt 500) AND
(time(0) gt 500) THEN PULSOUT 13, 650
' Left rotate PULSOUT 12, 650
ENDIF LOOP '
Repeat main loop.